There's no reason why you can't have three separate references in the main text all pointing to the exact same note/entry on your footnotes page. But it's not possible for the entry on your footnotes page to have some sort of "miracle link" that knows which of three possible origins to return to.

And if your three original references in the main text are all part of the same (x)html file, it's not possible to have duplicate IDs if you want your code to validate. An ID must be absolutely unique to that (x)html file.